In the production of micromechanical patterns or components, silicon is mostly used as a functional layer, based on its properties, which are superb for this application. This functional silicon layer may be supplemented by additional layers, for instance, oxide or nitride layers, whereby a build-up of multilayers may occur. A selective removal of a certain layer, for instance, a so-called sacrificial layer, on a silicon semiconductor substrate is a conventional measure in production methods of semiconductor components, especially in methods for producing self-supporting structures. In the production of micromechanical sensors, for example, a sacrificial layer is developed on a semiconductor substrate, onto which further patterned layers are deposited and patterned. This sacrificial layer is subsequently selectively removed to expose the further patterns. Frequently used sacrificial layers are silicon-germanium (SiGe) mixed semiconductor layers, since silicon-germanium layers are selectively removable from silicon layers. By the controlled removal of the sacrificial layer of SiGe, a self-supporting structure is generated that is situated on top of it.
In the case of using SiGe layers, in the further processing, the development of a diffusion barrier to adjacent layers based on silicon will become necessary, since in response to the exceeding of appropriate activating energies, such as in high temperature processes or tempering processes of the further sensor production, germanium would diffuse into adjacent silicon layers. Silicon oxide layers are suitable diffusion barriers, for example.
Besides exposing micromechanical patterns, such as sensor structures, using sacrificial layer etching of SiGe layers, the patterning of layer arrangements based on silicon is also indispensable in systems technology, above all for producing micromechanical patterns. Thus, besides the complete removal of a sacrificial layer, it is normally required to produce micromechanical patterns which have specified sidewall profiles, especially vertical sidewall profiles or conical sidewall profiles.
Such sidewall profiles are normally produced using a fluorine-based silicon deep-etching method that is described in German Patent No. DE 4241045 C1. In this case, the sidewalls, for instance, of sensor patterns to be produced are produced by complementing etching and passivating steps, using a teflon-type polymer as passivating agent and a fluorine-containing etching reagent. However, anisotropic plasma etching methods are very costly. Furthermore, such applied teflon-type protective layers onto the sidewalls of the patterns are often not sufficient for avoiding an etching attack during the plasma etching step.